1. Field of the Invention
The present invention relates generally to the field of microlens manufacturing. More particularly, the present invention relates to an assessing mark laid on the scribe lines, which is used to assess the conditions and quality of the microlens array.
2. Description of the Prior Art
Microlens technology is widely used in various optoelectronical products such as color digital cameras, and endoscopes. The microlens is used to control the traveling directions of each light ray, so that the light can be precisely converged or diverged upon light sensing areas. Furthermore, through the control of digital devices, light and electricity can be interchanged digitally with each other.
For example, the converged digital camera is usually constituted by superimposing color filter arrays (CFA) either on a charge-coupled device (CCD) image sensor or on a complementary metal-oxide-semiconductor (CMOS) image sensor. In general, CFA contains three or more color filter channels arranged alternately, where each color filter channel only lets light with a specific frequency pass through, projecting to the corresponding image sensor. Therefore, the color of the image is interpreted by CFA, and then transferred to each corresponding sensor device for further processing. Furthermore, microlens arrays coupled with CFA can be used to focus the light rays, so that either the layout area of each sensor device on the substrate can be increased or the integrity can be raised.
Referring to FIG. 1, illustrating the cross-sectional view of the prior art sensor chip structure containing the microlens array and the sensor device, light-sensitive regions 12 are formed in a chip substrate 10. Sensor devices 14, for example, CCD or CMOS, are formed on the substrate 10. A planarized transparent layer 16 is formed on the substrate 10, with a CFA layer 18 formed thereon. The microlens array 20 is formed above the CFA layer 18, which refract light rays 22 coming from the outside to focus on the light-sensitive regions 12. Typically, the microlens array 20 is fabricated using the process steps set forth in FIG. 2 to FIG. 4. First, a microlens resist layer 30 is coated over the CFA layer 18. A lithographic process is then carried out to form a microlens array 20 comprising a plurality of resist blocks 42. Subsequently, the resist blocks 42 are subjected to a thermal baking process, and are melted and cured to form semispherical shaped microlens 44.
Hitherto, none of the prior art provides a monitoring pattern in the scribe line region of a sensor chip or die for inspecting the baking conditions of the microlens array. Conventionally, to judge the conditions (baked or not baked) of the microlens, the wafer is put under an optical microscope, and the microlens array thereof is inspected by the human eye and sorted according to the reflected light patterns. However, as the microlens array gets thinner, it becomes more difficult to discern between the reflected light pattern before baking and that after baking. Furthermore, the aforesaid inspection method cannot assess the quality of the microlens after baking.